Career

Born, most
probably, in Béthune, France,
Buridan studied and later taught at the University of
Paris. Apocryphal stories abound about his reputed
amorous affairs and adventures which are enough to show that he
enjoyed a reputation as a glamorous and mysterious figure in Paris
life. In
particular, a rumour held that he was sentenced to be thrown in a
sack into the river Seine, but was
ultimately saved through the ingenuity of a student.François Villon alludes to this
in his famous poem Ballade des Dames du Temps
Jadis. Buridan also seems to have had an unusual facility for
attracting academic funding which suggests that he was indeed a
charismatic figure.

Unusually, he spent his academic life in the faculty of arts,
rather than obtaining the doctorate in theology that typically prepared the way for a
career in philosophy. He further
maintained his intellectual independence by remaining a secular cleric, rather than joining a
religious order. By 1340, his
confidence had grown sufficiently for him to launch an attack on
his predecessor, William of
Ockham. Buridan also wrote on solutions to paradoxes such as the liar
paradox. A posthumous campaign by Ockhamists succeeded
in having Buridan's writings placed on the Index Librorum Prohibitorum
from 1474-1481.

Impetus Theory

The concept of inertia was alien to the physics of
Aristotle. Aristotle, and his peripatetic followers, held that a body was only
maintained in motion by the action of a continuous external
force. Thus, in the Aristotelian view, a
projectile moving through the air would owe its continuing motion
to eddies or vibrations in the surrounding
medium, a phenomenon known as antiperistasis. In the absence of a
proximate force, the body would come to rest almost
immediately.

Jean Buridan, following in the footsteps of John Philoponus and Avicenna, proposed that motion was maintained by
some property of the body, imparted when it was set in motion.
Buridan named the motion-maintaining property impetus.
Moreover, he rejected the view that the impetus dissipated
spontaneously, asserting that a body would be arrested by the
forces of air resistance and gravity which
might be opposing its impetus. Buridan further held that the
impetus of a body increased with the speed with which it was set in
motion, and with its quantity of matter. Clearly, Buridan's impetus
is closely related to the modern concept of momentum. Buridan saw impetus as causing
the motion of the object. Buridan anticipated Isaac Newton when he wrote:

...after leaving the arm of the thrower, the projectile
would be moved by an impetus given to it by the thrower and would
continue to be moved as long as the impetus remained stronger than
the resistance, and would be of infinite duration were it not
diminished and corrupted by a contrary force resisting it or by
something inclining it to a contrary motion

Buridan used the theory of impetus to give an accurate qualitative
account of the motion of projectiles but he ultimately saw his
theory as a correction to Aristotle, maintaining core peripatetic
beliefs including a fundamental qualitative difference between
motion and rest.

The theory of impetus was also adapted to explain celestial phenomena in terms of
circular impetus.

Bibliography

Works by Buridan

Hughes, G.E. (1982) John Buridan on Self-Reference: Chapter
Eight of Buridan's Sophismata. An edition and translation with
an introduction, and philosophical commentary. Cambridge/London/New
York: Cambridge University Press, ISBN 0-521-28864-9.

King, Peter (1985) John Buridan's Logic: The Treatise on
Supposition; The Treatise on Consequences. Translation from
the Latin with a Philosophical Introduction, Dordrecht:
Reidel.

Zupko, John Alexander, ed.&tr. (1989) 'John Buridan's
Philosophy of Mind: An Edition and Translation of Book III of His '
Questions on Aristotle's De Anima (Third Redaction), with
Commentary and Critical and Interpretative Essays.' Doctoral
dissertation, Cornell University.